A) Field of the Invention
This invention relates generally to a rotational velocity sensor ring and method for forming the ring.
The invention is particularly applicable to and will be described with reference to a rotational velocity sensor ring for use in a speed sensor package mounted on a wheel bearing spindle of a vehicle for anti-lock and like purposes. However, those skilled in the art will recognize that the invention has broader application and can be applied in any number of industrial and non-vehicular applications in which the rotational movement of an object is to be detected.
B) Incorporation by Reference
The following patents are incorporated by reference herein and made a part hereof so that details related to wheel bearings, wheel bearing spindles and sensors used with sensor rings which are conventionally well known in the art need not be described in detail in the specification of this patent.
1) U.S. Pat. No. 5,696,442, issued Dec. 19, 1997 to Foster, et al., entitled xe2x80x9cROTATIONAL VELOCITY SENSOR RING APPARATUS AND METHODxe2x80x9d.
2) U.S. Pat. No. 5,111,138, issued May 5, 1992 to Kramer, entitled xe2x80x9cSPEED SENSOR HAVING A CLOSED MAGNETIC FLUX PATH FOR SENSING SPEED FROM AN AXIAL FACE OF A ROTATING MEMBERxe2x80x9d.
3) U.S. Pat. No. 5,010,290, issued Apr. 23, 1991 to Foster, entitled xe2x80x9cEASILY INSTALLED WHEEL BEARING SENSOR PACKAGExe2x80x9d.
4) U.S. Pat. No. 4,988,220, issued Jan. 29, 1991 to Christiansen et al., entitled xe2x80x9cSERVICABLE WHEEL SPEED SENSOR ASSEMBLYxe2x80x9d.
5) U.S. Pat. No. 4,795,278, issued Jan. 3, 1989 to Hayashi, entitled xe2x80x9cBEARING ASSEMBLYxe2x80x9d.
The material incorporated by reference herein does not, per se, form the present invention.
C) Prior Art
In a known manner of sensing rotational velocity of a rotating body, a sensor ring, also known as an encoder ring, exciter ring or tone ring, is mounted so that it rotates with the rotating body. A variable inductance or variable reluctance sensor is mounted concentrically around the sensor ring or, alternatively, proximate to one portion of the exterior of the sensor ring. The sensor is fixedly mounted and does not rotate with the sensor ring. The sensor includes circuitry configured to provide an output signal that varies with the rotational velocity of the sensor ring. Typically, as the rotational velocity of the sensor ring increases, the frequency of the output signal increases.
One known type of sensor ring comprises a machined or pressed metal ring with extending teeth substantially equally spaced around the outside perimeter of the ring. The sensor is configured so that when the ring is in certain positions, each tooth lines up with one or more poles of the sensor. When the ring is then turned from that position so that the teeth are no longer directly aligned with the pole, the sensor detects a change in inductance or reluctance of the magnetic circuit including the sensor poles and the sensor ring. It is through detecting such changes in inductance or reluctance that rotational velocity sensors operate.
For the most part, sensor rings have been formed from powdered metal sintered into a desired shape. Certain metals in the composites are selected for their magnetic properties. However, the prior art has recognized that plain carbon steels, (i.e., sheet metal stock or plain carbon steel with alloying elements for enhanced magnetic properties), has superior ferro-magnetic properties and does function, if properly formed, as rotational sensor rings. Plain carbon steel sensor rings have been fabricated in a variety of ways which can be generally classified or grouped in several categories.
One category can be explained as forming fingers on a rotating hub such as shown in U.S. Pat. No. 5,080,500, issued Jan. 14, 1992, which are difficult to handle in mass manufacturing and tend not to be durable. Accordingly, the fingers are strengthened by being bent back onto one another and formed into a ring such as shown in my prior ""442 patent cited above or interlocked together to form two hubs forming xe2x80x9cwindowsxe2x80x9d such as shown, for example, in U.S. Pat. No. 4,940,937, issued Jul. 10, 1990, which is generally not desirable.
Another category forms windows on a hub such as shown in the ""138 patent and U.S. Pat. No. 5,166,611, issued Nov. 24, 1992. In the ""278 patent, the windows are formed on a hub or on a hub which is formed as a cup or in one embodiment, a hub with a xe2x80x9cVxe2x80x9d shaped cross-section. The xe2x80x9cwindowsxe2x80x9d are formed between the ends or edges of the hub. In practice, it is difficult to form the shapes depicted from a blank without distorting the cylindrical hub and the windows.
Another type of sensor ring is shown in pictorial representation in prior art FIGS. 1A and 1B. This design has proven itself to be commercially durable, extremely rigid, and produces acceptable sensor signals. It is a variation of a design illustrated in the second embodiment disclosed in the ""442 patent. The sensor is produced from a stamped blank in which the hub 1 is drawn and a stepped xe2x80x9cUxe2x80x9d shaped sensor portion 2 as shown in prior art FIG. 1B is formed radially outward of hub 1. The outer leg 3 of the xe2x80x9cUxe2x80x9d is corrugated or formed with sine shaped undulations 3 as best shown in FIG. 1B. Undulations 3 have peaks 4 and valleys 5 which correspond to the xe2x80x9cwindowsxe2x80x9d discussed above. The sensor pickup head detects the changes in the magnetic flux density which is caused by the peaks and valleys and then detects the rotational velocity of the sensor ring.
All of the sensor rings discussed are functional and several have been commercially implemented. Each, however, have drawbacks and can be improved. For example, finger designs are suspect of being bent or distorted not only in use but simply in the handling and storing of a large number of rings inevitably occurring in the manufacturing process of a bearing assembly. Window designs are preferred for reasons discussed below but are difficult to accurately produce from a stamped blank with minimal forming steps. Variations in the window edges cause accuracy error in the sensor signal and may require revised sensor design and/or cause mounting restrictions. Corrugated sensor rings give limits to sensor sensitivity due to lack of sharp edges which tend to provide better flux changes.
Accordingly, it is one of the main objects of the invention to provide an improved sensor ring which can be formed from a metal blank of minimal mass while producing improved magnetic performance.
This object along with other features of the invention is achieved in a method of manufacturing a rotational velocity sensor ring which includes the steps of forming a flat ring-shaped blank from a sheet of ferro-magnetic metal stock and drawing a cylindrical hub portion from the radially inner portion of the ring blank so that the blank has an L-shaped, cross-sectional configuration with an annular sensor portion extending radially outward from the hub portion. In the drawn blank, a plurality of substantially identical, circumferentially spaced windows are punched in the sensor portion with each window having an inner edge adjacent to but spaced radially outward from the hub portion and an outer edge adjacent to and spaced radially inwardly from the outside edge of the sensor portion. Importantly, the sensor portion is bent along an imaginary bend circle adjacent the windows"" inner edges in the direction of the hub so that the blank now has a U-shaped, cross-sectional configuration while simultaneously forming an undulation in the sensor portion of the blank between the peripheral outer end of the sensor portion and the outer edge of each window whereby a symmetrically uniform sensor portion of the sensor ring is formed into a rigid structure from a blank with less metal or mass than that of the prior art.
In accordance with another important feature of the invention, the depth of the undulations formed in the bending step are precisely controlled to produce a sensor portion in the form of a substantially symmetrical cylinder or, alternatively, a substantially symmetrical frusto-conical sensor portion generally concentric with the hub portion of the ring whereby the sensor ring can be easily configured to match any number of anti-lock or like sensor mounting arrangements while maintaining a consistent air gap with the sensor during ring rotation to enhance sensor performance.
In accordance with another aspect of the invention, a one piece rotational velocity sensor ring is provided which includes a longitudinally-extending cylindrical hub portion and a sensor portion extending from the hub portion. The sensor portion has an annular bight segment extending radially outward from the hub portion and a generally cylindrical (or frusto-conical), longitudinally extending sensor segment extending from the bight segment and terminating an outer peripheral end. The sensor segment has a plurality of substantially identical window openings at equally spaced, circumferential increments therein with each window having an inner edge adjacent the hub portion and located within the bight segment, an outer edge adjacent to but spaced from the outer end of the sensor segment and a trailing and a spaced leading window edge extending between the inner and outer window edges, respectively. An undulation in the sensor segment between the outer end of the sensor segment and each window outer edge in combination with the windows results in a plurality of metal lands or teeth or fingers which extend between the trailing edge of one window and the leading edge of an adjacent window. The sensor lands are rigidized at one end by the bight sensor segment and at their other end by the undulations to provide a rigid ring which is not susceptible of being bent or distorted during handling or transport in mass assembly procedures while the open space provided by the windows between adjacent lands or fingers significantly enhances the magnetic permeability of the rings.
In accordance with yet another aspect of the invention, a rotational velocity sensor ring is provided which is formed from a ring having a stamped configuration bent into a final configuration. The stamped configuration of the ring has a flat annular sensor portion extending from a cylindrical hub portion to form an L-shaped cross-section with the sensor portion having a plurality of substantially identical window openings at equally spaced circumferential increments therein. Each window has an inner edge adjacent to and spaced radially outward from the hub, an outer edge adjacent to and spaced radially inward from the outer peripheral end of the sensor portion and a leading and trailing edge extending respectively from opposite ends of the inner and outer edges to form each window as a polygon, preferably a trapezoid. The sensor portion of the ring in the final configuration includes a bight sensor segment extending radially outward from the hub portion a distance beyond the inner edge and a sensor segment extending from the bight segment in the direction of the hub portion to form with the hub portion a U-shaped cross section with the sensor segment having an undulation between the outer edge of each window and the outer peripheral end whereby the leading and trailing edges of adjacent windows forming metal lands, teeth or fingers therebetween (circumferentially spaced about the ring) are substantially parallel to one another to produce consistent and clearly defined flux changes as the lands or fingers and the open spaced windows pass by the sensor head(s) when the sensor rotates.
In accordance with a more subtle but important feature of the invention, the geometric configuration of the window is correlated with the depth of the undulation to produce a desired spacing between the leading and trailing edges of adjacent metal lands or fingers. While the edges are preferably parallel to give precise demarcation flux changes as the magnetic flux lines pass from an open window space to a space occupied by a metallic finger or land, other configured edge relationships producing desired flux changes are possible. In all instances, the sensor pickup head is mounted between the undulations and the bight segment of the sensor portion, so that any influence on the flux fields caused by these metallic surfaces is minimized. Still further, the minimal effects on the magnetic permeability of the sensor ring caused by the undulations and the bight sensor segment are constant because of the irregular repeating patterns in the ring and the resulting noise is constant.
It is thus an object of the invention to provide a sensor ring formed with a minimal amount of metal.
It is another object of the invention to provide a sensor ring which has a configuration capable of providing improved or enhanced sensor performance.
In conjunction with the immediately preceding object, it is a specific object of the invention to provide a rotational sensor ring which allows for a wider air gap between sensor and ring at which the sensor can detect flux changes than conventional, metal stamped sensor rings.
In conjunction with the immediately preceding object, it is yet a more specific object of the invention to provide an improved rotational sensor ring which allows a greater freedom of sensor mounting and consequently an ability to mate a large variety of sensor packages in wheel bearing assemblies.
Yet another object of the invention is to provide a method for forming a rotational sensor ring which can readily produce conical as well as cylindrical sensor rings for use in a wide variety of wheel bearing assemblies.
Yet another object of the invention is to provide a rotational sensor ring which is stiff, durable and not readily deformable in the harsh automotive environment.
Still another specific object of the invention is to provide a formed metal rotational sensor ring which eliminates interlocking of individual parts which may otherwise occur in the ring manufacturing process or in the subsequent handling of a large number of the rings present when the rings are assembled onto wheel bearing spindles and the like.
A still further object of the invention is to provide a stamped metal rotational sensor ring which exhibits improved magnetic performance and contributes to the robustness of the sensor pickup unit when compared to existing stamped or powder metal sensor rings.
A general object of the invention is to provide a metal rotational sensor ring which is inexpensive and readily formed.
These and other objects, features and advantages of the invention will become apparent to those skilled in the art upon reading and understanding the Detailed Description of the Invention set forth below taken in conjunction with the drawings.